Testing for a leaking, ruptured, fuel pressure regulator diaphragm

That is a good analysis. How to verify the cause of an intermittent long crank and a start/stall condition. No need to have the electronics, just remove the vacuum hose and sniff if there is fuel smell or even fuel coming out. Watch for fuel. Takes over a minute that fuel is coming out of the port, diapraghm cracked. https://www.youtube.com/watch?v=AKtR_yF7bi8

Had that problem on my 1989 E32 750 which has 2 of them and with the old fuel rails the FPR's are pretty expensive. I did not have to wait that long as shown in the vid, pulled the vacuum hose from one of them and small and fuel dropped out, so it was really necessary to replace the old ones from 1989.

Symptoms of a Bad Fuel Pressure Regulator

If your fuel pressure regulator is going bad, your car could display several different symptoms. This article lists and explains the most common of these. Get your bad fuel pressure regulator checked if you notice any of the following.

Spark Plugs Blackened
Remove a spark plug and examine the end of it. If it is sooty, it could be a sign of a bad fuel pressure regulator. If you find a plug in this condition, check the rest of them. A sooty spark plug could just mean the engine is burning oil at that head.
If you end up replacing your fuel pressure regulator, you might also want to replace your plugs. They could be fouled out from the bad fuel pressure regulator. You can try simply cleaning them and putting them back, but if your engine still runs poorly, get new ones.

The Engine Doesn't Run Smoothly
Speaking of poor engine performance, if you are idling the engine and it is not running smoothly, change your oil filter and check your pressure regulator to repair bad fuel pressure. Another sign that your engine is suffering the effects of a bad fuel pressure regulator is if you have trouble starting the car. It will fail to turn over a few times before it actually starts.

The Tail Pipe Emits Black Smoke
Having black smoke coming out of your tail pipe is a sure sign there is something wrong with your fuel pressure regulator. Replace it. The normal color of any smoke coming out of the exhaust should be white or gray, not black, so if you see the latter, there is definitely something wrong.

The Dipstick Smells of Gasoline
Check the oil dipstick and see if you smell fuel on it. If you do, it could be a symptom of a bad fuel pressure regulator, which has allowed gasoline to leak into the oil system.

Engine Stalls
If the engine stalls when you press down on the gas pedal, check the fuel pressure regulator. There shouldn't be any hesitation when you press on the gas. Even if you only notice a little hesitation, get your pressure regulator checked out because it may just be starting to go bad.

Gasoline Is in the Vacuum Hose
If you are noticing any of the signs above, but aren't convinced that the cause is a bad fuel pressure regulator, there is something you can do to be sure one way or the other. Remove the vacuum hose that attaches to the fuel pressure regulator, making sure the engine isn't running. If gas is in the line, your fuel pressure regulator is bad. Also, if there is none in the line, but, when you turn the switch on, fuel drips out of the hose, it is bad.